The present invention relates to steering wheels for vehicles, and more particularly, to a mounting structure for a steering wheel having a ring cover, a spoke cover and a pad that are formed integrally.
A typical steering wheel includes an annular gripping ring and a pad. The pad is located at the center of the ring and connected to the ring by spokes. The spokes are integrally formed with a boss plate, which is coupled to a steering shaft. Japanese Unexamined Utility Model Publication No. 2-133955 describes a steering wheel having a ring cover, a spoke cover and a pad that are formed integrally. The boss plate of this steering wheel includes a male threaded fastener, and a corresponding threaded hole is formed axially in a steering shaft. The steering wheel is secured to the steering shaft by tightly threading the threaded fastener into the hole.
The ring cover, the spoke cover and the pad, which are formed integrally, limit the space in front of the boss plate. Therefore fastening the threads is troublesome. Japanese Unexamined Patent Publication No. 9-066843 describes a mounting structure for steering wheels to overcome this drawback. In this structure, splines are formed in a boss plate and corresponding splines are formed on a steering shaft. When installing the steering wheel on a steering shaft, the splines are initially engaged to mesh with each other. This fixes the rotational position of the steering wheel relative to the steering shaft. Thereafter, a threaded nut, which is connected to the boss plate, is fastened to a threaded distal end the steering shaft.
However, if the threaded distal end of the steering shaft is threaded into the nut when the splines are not yet securely meshed with each other, the steering wheel will not be firmly fixed to the steering shaft and chattering may occur. Therefore, the splines need to be fully meshed with each other before tightening the threads. This complicates the assembly of the steering wheel and lengthens the assembly process.